钻杆重金属污染致裂分析

Analysis of Drill Pipe's Crack Caused by Heavy Metal Pollution

试验分析了一批失效钻杆的化学成分、力学性能、金相和断口。结果表明,失效钻杆的裂纹均为沿晶裂纹,在裂纹扩展的晶界处发现含有较高的铅、锡、锑低熔点元素的白色块状物。对钻杆生产过程中的每道工序进行排查和分析后发现:在钻杆管经磁粉探伤工序时,由于磁化电流过大或接触不良而起弧造成了局部高温,使得磁化低熔点Pb-Sn-Sb电极熔化后附着在钢管上,在经过钻杆的后续摩擦焊和内涂层加热保温后,铅、锡、锑沿晶界扩散渗透到钢管基体内部,在外力作用下形成裂纹源。

The chemical composition, mechanical properties, metallographic phase and fracture of off-grade drill pipes were investigated. The results show that all the cracks of drill pipes are intergranular cracks, white blocks riched in Pb, Sn and Sb were found in the grain boundary of the cracks. Through inspecting and analyzing of every process in drill pipes＇ fabrication, it can be seen that local high temperature were produced by excessive magnetization current or arcing electrode and lowing-melting point Pb-Sn-Sb magnetization electrode melted and attached on the pipe during magnetic powder inspection process. After the following friction welding and internal coating, Pb, Sn and Sb diffused into the pipe substrate and formed crack source under the action of an external force.